If you have connected your iPhone, Android or Windows smartphone address books to the Facebook App, there is a chance that your contacts’ email addresses are now set to send to the user’s Facebook address rather than their “normal” email account.

When you synch your phone with your PC or laptop these changes will also be made in your main address book.

Given most people don’t use their Facebook supplied email this means many people won’t see messages sent to that address. This is a serious problem

You can check if your address book has been changed by simply looking at your contacts’ email addresses.

Facebook’s behaviour on this is seriously worrying, it’s bad enough they store all of our data but altering our personal information is for me a bridge too far.

Given most mobile phone users would rather have their wallet stolen than lose their handset, Facebook’s messing with phones address book is going to shake their confidence in the service far more than the myriad privacy issues.

If the IPO was Facebook’s peak, it could well be this poorly thought out tactic that marks the beginning of the company’s decline.